Bad request on attempt to update Wiki page

Using C#

{
// Get content by page ID
PageContent pageContent = await GetContentAsync(url);

// pageContent: {Body: null, Id: “900334136”, Title: “GF Test page”, Type: “page”, Version: {Number: 5}}

// new version
Version ver = pageContent.Version;
ver.Number += 1;

// Extract body
pageContent = await GetContentAsync(url + “?expand=body.storage”);

// Updating just title
pageContent.Version = ver;
pageContent.Title = pageContent.Title + “QQQ”;

// pageContent: {Body: {Storage: {Representation: “storage”, Value “

some text

”}, Id: “900334136”, Title: “GF Test pageQQQ”, Type: “page”, Version: {Number: 6}}

PageContent newContent = await UpdateProductAsync(url, pageContent);

// - fails with 400, “Bad request”
}

static async Task UpdateContentAsync(string path, PageContent content)
{
HttpResponseMessage response = await client.PutAsJsonAsync(path, content);
response.EnsureSuccessStatusCode();

// Deserialize the updated content from the response body.
content = await response.Content.ReadAsAsync();
return content;
}

Any ideas why it does not work?
Thanks

Resolved.
As soon as I have turned all DTO members names to lowercase - worked.
I.e. “type: “page”, version: {number: 5}”
instead of
“Type: “page”, Version: {Number: 5}”
etc.